This invention relates to a process and apparatus for the separation of C.sub.2+ or C.sub.3+ hydrocarbons from a gas stream containing light hydrocarbons, wherein the gas stream, under super atmospheric pressure, is cooled, partially condensed and separated into a liquid and a gaseous fraction, and wherein the liquid fraction is subjected to rectification to obtain a product stream containing essentially C.sub.2+ or C.sub.3+ hydrocarbons and a residual gas stream containing predominantly lower boiling components. By light hydrocarbons is generally meant aliphatic hydrocarbons containing 1-5 carbon atoms.
Such processes are used mainly to separate ethane or propane from natural gases or other gases, for example refinery tail gases. In addition, these processes are suitable for the separation of analogous unsaturated hydrocarbons, for example ethylene or propylene, from a gas stream containing these components, for example, refinery tail gases. Reprocessing of refinery tail gases has recently become economically attractive since the market prices for LPG (C.sub.3 /C.sub.4 hydrocarbon mixtures) have increased while, in contrast, the demand for vacuum residues such as heavy oil has decreased. For this reason, heavy fractions are often burned to cover the internal fuel needs of a refinery whereas the C.sub.2+ or C.sub.3+ hydrocarbons which collect in large amounts, especially in the processing of light crude oil components into gasoline, are separated from tail gases.
In an earlier German patent application P 34 08 760.5 filed Mar. 9, 1985, having a common assignee and corresponding substantially to U.S. application Ser. No. 709,742 filed Mar. 8, 1985 by Bauer et al, incorporated by reference herein, a process of this type is disclosed which relates to the separation of C.sub.3+ hydrocarbons. An important feature of this earlier application resides in the fact that the C.sub.3+ hydrocarbons to be separated condense out during the partial condensation to such an extent that only the condensate needs to be fed into the rectification, while the uncondensed portions contain so little C.sub.3+ hydrocarbons that further condensation can be dispensed with. Because of this, the uncondensed portions can be immediately heated again, preferably in indirect exchange with feed gas, and thereafter removed as a residual gas without first having to go through rectification. That leads to more advantageous rectification conditions, particularly since a higher overhead temperature can be used.